Method and an apparatus for processing a video signal

ABSTRACT

A method of processing a video signal is disclosed. The present invention includes obtaining a current macroblock type, obtaining skip or direct mode indication information on a partition of the current macroblock according to the current macroblock type, deriving a motion vector of the partition according to the skip or direct mode indication information, and predicting a pixel value of the partition using the motion vector. Accordingly, the present invention obtains a pixel value of a reference block close to an original video using a motion vector, thereby enhancing a reconstruction ratio of the macroblock. As a macroblock uses skip or direct prediction indication information, it is unnecessary to separately code skip mode indication information and direct mode indication information on the macroblock, whereby an information size to be coded can be reduced.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/205,591, filed Mar. 12, 2014, now allowed, which is a continuation ofU.S. application Ser. No. 12/574,415, filed Oct. 6, 2009, now U.S. Pat.No. 8,699,562, which claims the benefit of U.S. Provisional ApplicationNo. 61/103,221 filed on Oct. 6, 2008, U.S. Provisional Application No.61/119,697, filed on Dec. 3, 2008, U.S. Provisional Application No.61/120,060, filed on Dec. 5, 2008, U.S. Provisional Application No.61/143,813, filed on Jan. 11, 2009, U.S. Provisional Application No.61/154,420 filed on Feb. 22, 2009, U.S. Provisional Application No.61/159,058 filed on Mar. 10, 2009, Korean Application No.10-2009-0094486 filed on Oct. 6, 2009, all of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an apparatus for processing a videosignal and method thereof, for which inter picture prediction is used.

Discussion of the Related Art

Generally, in transmitting an encoded video signal to a decoder, amethod of removing spatial redundancy and temporal redundancy, i.e.,intra or inter picture prediction is performed to enhance a compressionratio of the video signal.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an apparatus forprocessing a video signal and method thereof that substantially obviateone or more of the problems due to limitations and disadvantages of therelated art.

An object of the present invention is to provide an apparatus forprocessing a video signal and method thereof, by which a video signalcan be efficiently processed using inter picture prediction.

Another object of the present invention is to provide an apparatus forprocessing a video signal and method thereof, by which a video signalcan be efficiently processed in a manner of performing inter pictureprediction using a skip mode.

A further object of the present invention is to provide an apparatus forprocessing a video signal and method thereof, by which a video signalcan be efficiently processed using a direct mode.

To achieve these and other advantages, the present invention proposes avideo signal processing method characterized in configuring variousmotion vector candidates in performing inter picture prediction andobtaining a precise motion vector from the various motion vectorcandidates.

The present invention proposes a video signal processing methodcharacterized in indicating whether a region having a predetermined sizewithin a macroblock is coded in a skip mode.

The present invention proposes a video signal processing methodcharacterized in indicating whether a partition of a macroblockaccording to macroblock type information is coded in a skip mode.

The present invention proposes a video signal processing methodcharacterized in proposing a macroblock type for indicating a skip modeor a direct mode in part within one macroblock and performing interpicture prediction using the skip mode or the direct mode based on themacroblock type.

The present invention proposes a video signal processing methodcharacterized in deriving a motion vector by a block unit smaller than asize of a macroblock if the macroblock is coded in a skip mode.

And, the present invention proposes a video signal processing methodcharacterized in defining skip mode indication information or directmode indication information, indicating whether a macroblock is coded ina skip mode, and determining whether it is a skip mode or a direct modeusing CBP (coded block pattern) information.

Accordingly, the present invention provides the following effects and/oradvantages.

First of all, a precise motion vector is obtained from motion vectorcandidates for inter picture prediction. Hence, a bit size of a motionvector difference value to be coded can be reduced and accuracy inreconstructing an original video can be enhanced. In case that a skipmode or a direct mode is used for a macroblock greater than 16×16, bymeans of using a skip mode or a direct mode by a block unit smaller thana size of the macroblock, error of inter picture prediction using a skipmode or a direct mode can be reduced and coding efficiency can beenhanced. By means of using a macroblock type for indicating a skip modeor a direct mode within one macroblock partially, it is not necessary tocode information indicating a skip mode or a direct mode for apredetermined-size region within the macroblock and it is also able toreduce a bit size to be coded by coding the macroblock type informationonly. In case of coding a macroblock in a skip mode, by a motion vectoris derived by a block unit smaller than a size of the macroblock, it isable to obtain a pixel value of a reference block close to an originalvideo using the motion vector. Accordingly, it is able to improve areconstruction ratio of a macroblock. As a macroblock uses a skip modeor a direct mode, it is not necessary to separately code skip modeindication information and direct mode indication information separatelyfor a macroblock. Since a skip mode or a direct mode is determined usingalready-coded CBP information, it is able to reduce an information sizeto be coded. Therefore, efficiency of video signal processing can beenhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a schematic block diagram of a video signal decoding apparatusaccording to the present invention;

FIG. 2 is a diagram for a method of applying a skip mode by a block unitsmaller than a size of a macroblock according to one embodiment of thepresent invention;

FIG. 3 is a block diagram for a method of indicating a portion that usesa skip mode within a macroblock based on macroblock type information;

FIG. 4 is a diagram for a method of indicating whether a currentmacroblock is partially coded in a skip mode at a sub-macroblock levelaccording to one embodiment of the present invention;

FIG. 5 is a diagram for a method of indicating whether a currentmacroblock is partially coded in a skip mode according to anotherembodiment of the present invention;

FIG. 6 and FIG. 7 are diagrams of a macroblock type for indicating apartial skip mode according to one embodiment of the present invention;

FIG. 8 is a diagram for a method of deriving a motion vector in casethat a macroblock type is a P skip macroblock according to oneembodiment of the present invention;

FIG. 9 is a schematic internal block diagram of an inter prediction unit700 having a spatial direction prediction mode applied thereto; and

FIG. 10 is a block diagram of a process for decoding slice data usingskip or direct mode indication information.

DETAILED DESCRIPTION OF THE INVENTION

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method ofprocessing a video signal includes the steps of obtaining currentmacroblock type, obtaining skip or direct mode indication information ona partition of the current macroblock according to the currentmacroblock type, deriving a motion vector of the partition according tothe skip or direct mode indication information, and predicting a pixelvalue of the partition using the motion vector.

Preferably, the present invention is characterized in that the skip ordirect mode indication information includes information indicatingwhether the partition is coded in a skip mode or a direct mode.

Preferably, the present invention is characterized in that the step ofderiving the motion vector of the partition further includes the stepsof obtaining CBP (coded block pattern) information of the currentmacroblock and determining whether the partition is coded in a skip modeor a direct mode based on the CBP information.

More preferably, the present invention is characterized in that themethod further includes the step of if the partition is coded in thedirect mode, obtaining residual data of the partition.

In this case, the present invention is characterized in that theresidual data of the partition means a difference value between anoriginal pixel value of the partition and the predicted pixel value.

Preferably, the present invention is characterized in that the motionvector of the partition is derived from an medium value of a motionvector of a block neighbor to the partition.

More preferably, the present invention is characterized in that theblock neighbor to the partition includes left, top and right top blocksof the partition.

Preferably, the present invention is characterized in that the pixelvalue of the partition includes a pixel value of a reference blockindicated by the motion vector of the partition.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. First of all, terminologies or words used in thisspecification and claims are not construed as limited to the general ordictionary meanings and should be construed as the meanings and conceptsmatching the technical idea of the present invention based on theprinciple that an inventor is able to appropriately define the conceptsof the terminologies to describe the inventor's invention in best way.The embodiment disclosed in this disclosure and configurations shown inthe accompanying drawings are just one preferred embodiment and do notrepresent all technical idea of the present invention. Therefore, it isunderstood that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents at the timing point of filing thisapplication.

First of all, a macroblock is a basic unit for processing a video frameand can be defined as a region constructed with 16×16 pixels. Amacroblock greater than 16×16 can becomes a basic unit for processing avideo frame having resolution higher than that of the related art. Forinstance, this macroblock can be defined as a region constructed with32×32 pixels or 64×64 pixels for examples.

A macroblock greater than 16×16 can be adaptively used according toresolution of a video image. For instance, if resolution of a videoimage is equal to or smaller than VGA, it is able to set a size of amacroblock to 16×16. Accordingly, one of 16×8, 8×16, 4×8, 8×4 and 4×4blocks is usable as a partition of a macroblock. If resolution of avideo image is equal to or greater than VGA and equal to or smaller than1080P, it is able to set a size of a macroblock to 32×32. Accordingly,one of 32×16, 16×32, 16×16, 16×8, 8×16 and 8×8 blocks is usable as apartition of a macroblock. If resolution of a video image is equal to orgreater than 1080P and equal to or smaller than 4k×2k, it is able to seta size of a macroblock to 64×64. Likewise, one of 64×32, 32×64, 32×32,32×16, 16×32 and 16×16 blocks is usable as a partition of a macroblock.Yet, an encoder is able to determine an optimal size of one of a 16×16macroblock and other macroblocks greater than 16×16 according toresolution of a video image. The determined macroblock size informationcan be transmitted to a decoder at a slice or sequence level.

A macroblock type can be defined according to a prediction mode of amacroblock, i.e., according to an intra picture prediction mode or aninter picture prediction mode. This can include size information of apredicted block. And, a macroblock type for performing inter pictureprediction can include information on a prediction direction as well.

A size of a predicted block coded in an intra picture prediction modecan be set to one of 16×16 pixels, 8×8 pixels and 4×4 pixels. Thepredicted block can means a unit of a block for performing intra pictureprediction or inter picture prediction within a picture. For the motioncompensation of a predicted block coded in the inter picture predictionmode, one of 16×16 pixels, 16×8 pixels, 8×16 pixels and 8×8 pixels isusable as a size of the predicted block. In case that 8×8 pixels areused as a size of a predicted block, it is able to perform inter pictureprediction by a unit of partition (e.g., 8×4 pixels, 4×8 pixels and 4×4pixels) of the 8×8 pixels predicted block.

In case that resolution is equal to or greater than VGA and equal to orsmaller than 1080P, a size of a predicted block coded in an intrapicture prediction mode can be set to 16×16 pixels or 8×8 pixels. And, asize of a predicted block coded in an inter picture prediction mode canbe set to one of 16×16 pixels, 16×8 pixels, 8×16 pixels and 8×8 pixels.In this case, inter picture prediction may not be performed by a unit ofa partition (e.g., 8×4 pixels, 4×8 pixels and 4×4 pixels) of an 8×8pixels predicted block. In case that resolution is equal to or greaterthan 1080P and equal to or smaller than 4 k×2 k, a size of a predictedblock coded in an intra picture prediction mode or an inter pictureprediction mode can be set to 16×16 pixels.

Likewise, an encoder is able to determine an optimal macroblock typeaccording to resolution of a video image. This determined macroblocktype information can be sent to a decoder at a slice level or a sequencelevel. Accordingly, it is able to adaptively use the determinedmacroblock type.

FIG. 1 is a schematic block diagram of a video signal decoding apparatusaccording to the present invention.

Referring to FIG. 1, the decoding apparatus mainly includes a parsingunit 100, an entropy decoding unit 200, a inverse quantizing/inversetransform unit 300, an intra prediction unit 400, a deblocking filteringunit 500, a decoded picture buffering unit 600, an inter prediction unit700 and the like.

The parsing unit 100 performs parsing by NAL unit to decode a receivedvideo image. Generally, at least one or more sequence parameter sets andpicture parameter sets are sent to a decoder before a slice header anddata are decoded. In this case, various kinds of attribute informationscan be included in a NAL header region or an extension region of a NALheader. A parsed bitstream is entropy-decoded via the entropy decodingunit 200 and a coefficient of each macroblock, a motion vector and thelike are then extracted. The inverse quantizing/inverse transform unit300 obtains a coefficient value by multiplying a received quantizedvalue by a predetermined constant and then reconstructs a pixel value byinverse-transforming the coefficient value. The intra prediction unit400 performs intra picture prediction from a decoded sample within acurrent picture using the reconstructed pixel value. Meanwhile, thedeblocking filtering unit 500 is applied to each coded macroblock toreduce block distortion. A filter enhances an image quality of a frameby smoothing edges of a block. Selection for a filtering process dependson a variation of an image sample. Filtered pictures are outputted orstored in the decoded picture buffer unit 600 to be used as a referencepicture. The decoded picture buffer unit 600 plays a role in storing oropening previously coded pictures to perform inter picture prediction.In this case, in order to store or open them, frame num of each pictureand POC (picture order count) are used. The inter prediction unit 700performs inter picture prediction using the reference pictures stored inthe decoded picture buffer unit 600. A macroblock coded in an inter modecan be divided into macroblock partitions. And, each of the macroblockpartitions can be predicted from one or two reference pictures. Theinter prediction unit 700 compensates for a motion of a current blockusing informations transmitted from the entropy decoding unit 200. Inthe following description, it is understood that a block includes amacroblock or a partition of a macroblock. Motion vectors of blocksneighbor to a current block are extracted from a video signal. It isthen able to obtain a motion vector predicted value of the current blockfrom the neighbor block. The neighbor block can include a block at aleft, top or right top side of the current block. For instance, it isable to set a predicted value of a motion vector of a current block tobe obtained using medium values of horizontal and vertical components ofmotion vectors of neighbor blocks. Alternatively, in case that a leftblock of a current block has at least one predicted block coded in aninter picture prediction mode, it is able to set a predicted value of amotion vector of a current block to be obtained using a motion vector ofa predicted block located at a top side. In case that a top side blockof a current block has at least one predicted block coded in an interpicture prediction mode, it is able to set a predicted value of a motionvector of the current block to be obtained using a motion vector of apredicted block located at a most left side. In case that blocks locatedat top and right sides of a current block among neighbor blocks arelocated outside a boundary of a picture or slice, it is able to set apredicted value of a motion vector of the current block to a motionvector of a left block. If there exists one block having the samereference picture index of a current block among neighbor blocks, it isable to set a motion vector of the corresponding block to be used forprediction.

Based on a partition of a macroblock according to a macroblock type, itis able to obtain a predicted value of a motion vector. For instance,when a partition of the current macroblock according to a currentmacroblock type is 8×16, if an index of the partition of the macroblockis set to 0, it is able to set a top side block of a current block to beused for prediction. If an index of the partition of the macroblock isset to 1, it is able to set a left side block of a current block to beused for prediction.

In obtaining a motion vector predicted value of a current block, it isable to define various kinds of motion vectors extractable from neighborblocks as candidates for a motion vector predicted value. As mentionedin the foregoing description, the candidates for the motion vectorpredicted value can include a motion vector of one of neighbor blocks, amedium value of motion vectors of neighbor blocks and the like, by whichthe candidates are non-limited. Accordingly, an encoder selects a motionvector having best efficiency as a motion vector predicted value fromthe candidates for the motion vector predicted value and is then able tosend the selected motion vector information to a decoder. The selectedmotion vector information can be obtained from a slice level of amacroblock level. It is able to define the candidate of the motionvector predicted value using an index. And, the selected motion vectorinformation can include this index.

By coding a difference vector between a motion vector of a current blockand a predicted value of a motion vector, it is able to reduce a size ofbits to be coded. Using the obtained motion vector predicted value andthe difference vector extracted from a video signal, the motion of thecurrent block is compensated. Moreover, this motion compensation can beperformed using one reference picture or a plurality of pictures.

In case that a size of a macroblock is 16×16, total 7 kinds of blocksizes including 16×16, 16×8, 8×16, 8×8, 8×4, 4×8, and 4×4 are availablefor inter picture prediction. They can be hierarchically represented asmacroblock or sub-macroblock types. In particular, a size of a predictedblock can be represented as a macroblock type and one of 16×16, 16×8,8×16 and 8×8 can be selected.

A reference picture index and a motion vector can be coded for eachpredicted block. Alternatively, a motion vector can be coded for eachpredicted block. Of course, a coding scheme for a sub-macroblock can bedetermined in the same manner of a macroblock.

In reconstructing a current macroblock, a skip macroblock can be definedas using a pixel value of a macroblock intactly within a previouslycoded reference picture instead of having information on the currentmacroblock, i.e., a motion vector, a reference picture index and aresidual data. In coding a skip macroblock, a motion compensation usinga motion vector can be accompanied. This motion vector can be derivedusing a neighbor block. The former motion vector deriving method isidentically applicable to a method of deriving the motion vector.

A process for coding slice data using a skip mode is explained asfollows.

First of all, it is able to obtain flag information indicating whether acurrent macroblock within a slice is a skip macroblock.

In case of a macroblock greater than 16×16, it is able to apply a skipmode by a block unit smaller than a size of the macroblock by indicatinga partition of the macroblock that uses a skip mode. Hence, it is ableto enhance efficiency of coding.

FIG. 2 is a diagram for a method of applying a skip mode by a block unitsmaller than a size of a macroblock according to one embodiment of thepresent invention.

Referring to FIG. 2, in case that a size of a macroblock is 32×32, it isable to use flag information indicating whether it is a skip macroblockby 16×16 block unit. If a flag indicating whether it is the skipmacroblock is set to 1, it is able to define the macroblock is in a skipmode. In case that a partition of a macroblock located at a left topside within a macroblock is coded in a skip mode only, four bits ‘1000’can be transmitted. If all partitions of 16×16 macroblock within amacroblock are coded in a skip mode, other information such as a motionvector and the like is not parsed. Yet, if the macroblock partiallyincludes the partition of the macroblock coded in the skip mode, amacroblock type will be parsed. In this case, it can be represented as amacroblock type having a partition of 16×16 macroblock.

FIG. 3 is a block diagram for a method of indicating a portion that usesa skip mode within a macroblock based on macroblock type information.

Referring to FIG. 3, flag information indicating whether a current blockis a skip macroblock at a slice level is parsed [S300]. As a result ofthe parsing, if the current macroblock is not the skip macroblock [‘no1’], current macroblock type information will be parsed at a macroblocklevel [S310]. If the current macroblock is not the skip macroblock, someof partitions of the current macroblock may be coded in a skip mode.Hence, if the current macroblock is the skip macroblock [‘yes 1’], it isable to perform decoding without parsing motion information of thecurrent macroblock and the like [S340]. If the current macroblock is notthe skip macroblock, a current macroblock type is parsed and partitioninformation of the current macroblock can be then obtained from thecurrent macroblock type. It is able to parse flag information indicatingwhether a partition of the current macroblock is coded in a skip mode[S320]. When a size of a current macroblock is 32×32, as a result ofparsing a current macroblock type at a macroblock level, if the currentmacroblock type is represented as 16×16, it is able to parse flaginformation indicating whether partitions of the 16×16 macroblock arecoded in skip mode. According to the flag information, decoding will beperformed on the skip mode coded partition [‘yes 2’] without parsingmotion information and the like. And, motion information and residualdata will b parsed for the partition [‘no 2’] that is not coded in theskip mode [S330]. This can be identically applied to a sub-macroblocklevel.

FIG. 4 is a diagram for a method of indicating whether a currentmacroblock is partially coded in a skip mode at a sub-macroblock levelaccording to one embodiment of the present invention. Referring to FIG.4, if a size of a current macroblock is 32×32, it is able to set a sizeof a sub-macroblock to 16×16. As a result of parsing current macroblocktype information, if a partition of a macroblock according to a currentmacroblock type is 16×16, it is able to parse flag informationindicating whether four 16×16 sub-macroblocks are coded in skip mode[S400]. As a result of this parsing, it is able to perform decoding on askip-mode coded sub-macroblock without parsing separate information[S410]. Hence, it is able to parse a motion vector and reference pictureindex of this sub-macroblock [S420]. Yet, the motion vector of thesub-macroblock can be parsed based on a partition off the sub-macroblockaccording to a sub-macroblock type.

FIG. 5 is a diagram for a method of indicating whether a currentmacroblock is partially coded in a skip mode according to anotherembodiment of the present invention.

Referring to FIG. 5, it is able to parse flag information indicatingwhether a current macroblock within a slice is a skip macroblock [S500].If the current macroblock is the skip macroblock according to the flaginformation [‘yes 1’], it is able to perform decoding without parsingmotion information and the like [S550]. Yet, if the current macroblockis not the skip macroblock [‘no 1’], it is able to parse flaginformation indicating a presence or non-presence of a partition of thecurrent macroblock and a presence or non-presence of skip mode coding ofthe partition [S510].

For instance, in case that a size of a macroblock is 32×32, if the flagis set to 1, it is able to define that the partition of the macroblockis 16×16. And, it is also able to define that at least one of partitionsof the macroblock is coded in a skip mode. On the contrary, if the flagis set to 0, it is able to define that the partition of the macroblockis not 16×16 or define that all partitions of the macroblock are notcoded in the skip mode despite 16×16.

In the following description, assume that the flag is defined in theabove manner Hence, as a result of parsing the flag information, if ‘1’is obtained [‘yes 2’], as a partition of the macroblock is set to 16×16,it is not necessary to parse the macroblock type information. And, it isable to parse flag information indicating whether the partition of the16×16 macroblock is coded in the skip mode for four 16×16 macroblockpartitions [S560]. Hence, if the partition of the 16×16 macroblock iscoded in the skip mode [‘yes 3’], it is able to perform decoding withoutparsing motion information and the like [S550]. Moreover, if thepartition is coded in the skip mode, CBP information may not b parsed.Accordingly, by reducing a size of transmitted information, it is ableto enhance efficiency of signal processing. Yet, if not coded in theskip mode [‘no 3’], motion information and residual are parsed [S540]and it is able to decode using the parsing result [S550].

As a result of parsing the flag information, if 0 is obtained [‘no 2’],it is able to parse the current macroblock type information [S520]. If apartition of the current macroblock according to a current macroblocktype is not 16×16, it is able to parse flag information indicatingwhether it is coded in a skip mode [S530]. Yet, if a partition of thecurrent macroblock according to a current macroblock type is 16×16, asall four partitions are not coded in the skip mode, the flag informationindicating whether the partition is coded in the skip mode may not beparsed. And, it is able to set the information indicating whether thepartition is coded in the skip mode to be derived into 0.

If the partition is coded in the skip mode according to the flaginformation indicating whether each of the obtained partitions of themacroblock is coded in the skip mode [‘yes 3’], it is able to performdecoding without parsing motion information and the like. If thepartition is not coded in the skip mode [‘no 3’], it is able to performdecoding by parsing motion information and residual [S540] [S550].

In another way, it is able to newly define a macroblock type for a skipmode indication. FIG. 6 and FIG. 7 are diagrams of a macroblock type forindicating a partial skip mode according to one embodiment of thepresent invention.

In case that a size of a macroblock is greater than 16×16, it is able todefine a macroblock type that indicates whether a skip mode is used by apartition unit of the macroblock.

With reference to FIG. 6, explained in the following description is acase that a skip mode is used by a partition unit of a macroblock on theassumption that a size of a macroblock is 32×32. As mentioned in theforegoing description, in case that all partitions of the 16×16macroblock within a current macroblock are coded in the skip mode, it isable to obtain flag information indicating that a current macroblock isa skip macroblock at a slice level. On the contrary, in case that allpartitions of the 16×16 macroblock are not coded in the skip mode, flaginformation indicating that a current macroblock is not a skipmacroblock and the current macroblock type can be then parsed. In thiscase, if some of the partitions of the 16×16 macroblock are coded in theskip mode in part, a current macroblock type can be represented as amacroblock type proposed in FIG. 7. In particular, partitions (partitionindexes 0 and 2 of a macroblock) of the 16×16 macroblock are coded inthe skip mode and partitions (partition indexes 1 and 3 of a macroblock)of the 16×16 macroblock are not coded in the skip mode, a currentmacroblock type will become 5 [S600]. In this case, the partitions(partition indexes 0 and 2 of a macroblock) of the 16×16 macroblock canbe decoded without parsing other information such as motion informationand the like. Yet, motion info nation, reference picture indexes and thelike will be parsed for the partitions (partition indexes 1 and 3 of amacroblock) of the 16×16 macroblock. Each of the partitions (partitionindexes 0 and 2 of a macroblock) of the 16×16 macroblock can be set to asize of 16×32 predicted block or a size of 16×16 predicted block.

A method of deriving a motion vector of a skip macroblock is explainedas follows. And, a motion vector of a sub-macroblock can be derived inthe same manner.

First of all, if a current block is a skip macroblock, it is able toderive a motion vector using a neighbor block of the current block.

For instance, assume that a block at a left side of a current block, ablock at a top side and a block at a right top side are named a neighborblock A, a neighbor block B and a neighbor block C, respectively. And,assume that their motion vectors are set to mvA, mvB and mvC,respectively. A motion vector of the current block can be derived intomedium values of horizontal and vertical components of the mvA, mvB andmvC or an average value of the mvA, mvB and mvC. It can be derived intoone of three motion vectors and this can be determined based on areference picture index. Moreover, in case of a macroblock greater than16×16, it is ale to obtain a precise motion vector of a macroblock byderiving a motion vector by a block unit smaller than a size of themacroblock or the sub-macroblock.

FIG. 8 is a diagram for a method of deriving a motion vector in casethat a macroblock type is a P skip macroblock according to oneembodiment of the present invention.

Referring to FIG. 8, in case that a size of a macroblock is 32×32, it isable to derive a motion vector by a block unit smaller than a size ofthe macroblock, i.e., by 8×8 block unit. In particular, a motion vectorof a block 0 can be derived into an medium value of horizontal andvertical components of mvA0, mvB0 and mvC0, an average value of mvA0,mvB0 and mvB1, or one motion vector among mvA0, mvB0 and mvB1. Likewise,a motion vector of a block 1 can be derived into a medium value ofhorizontal and vertical component of mvB0, mvB1 and mvB2. Index of theblock may mean a decoding order.

Inter picture prediction using a direct mode is explained as follows.First of all, a direct mode indicates a mode for predicting motioninformation of a current block from motion information of areconstructed block. The motion information may include a motion vectorand a reference picture index. For instance, it is able to define apicture having a smallest reference index among List1 reference picturesas an anchor picture in a direct mode. And, a block of the anchorpicture co-located at the same spatial position of the current block canbe defined as an anchor block.

For instance, in a temporal prediction mode, it is able to predictmotion information of a current block using motion information of theanchor block. It is able to define a motion vector in a List0 directionof the anchor block as mvCo1. In this case, if a motion vector in theList0 direction of the anchor block does not exist but a motion vectorin List1 direction exists, it is able set a motion vector in the List1direction to mvCo1. In this case, in case of a picture B, it is able totwo random pictures can be used as reference pictures irrespective oftemporal or spatial sequence. In doing so, the used prediction is namedList0 prediction or List1 prediction. For instance, the List0 predictionmeans prediction for a forward direction, while the List1 predictionmeans prediction for a backward direction.

In a temporal direct mode, List0 reference picture of a current blockbecomes a picture referred to by the mvCo1 and List1 reference picturebecomes an anchor picture. If the anchor block does not have motioninformation, a motion vector becomes 0 and a reference picture index ofthe List0 reference picture in the temporal direct mode becomes 0.

Moreover, it is able to find a motion vector mvL0 of List0 and a motionvector mvL1 of List1 from the motion vector mvCo1. Assuming that a speedof motion within a reference picture, a current picture and an anchorpicture is constant, a size of each of the mvL0 and the mvL1 becomesproportional to time intervals among the reference, current and anchorpictures. Hence, using the interval between the reference picture andthe current picture and the interval between the reference picture andthe anchor picture, it is able to find the mvL0 and the mvL1. Inparticular, in case that List0 reference index of the anchor blockrefers to a long-term reference picture, it can be found by Formula 1.mvL0=mvCo1mvL1=0  Formula 1

In case that List0 reference index of the anchor block does not refers ta long-term reference picture, it can be found by Formula 2.mvL0=mvCo1*(tb/td)mvL1=−mvCo1*(td−tb)/td=mvL0−mvCo1  Formula 2

For another example of the direct mode, a spatial direct mode predictsmotion information of a current block using motion informationcorrelation of a spatial direction. Like the temporal direct mode, ananchor picture and an anchor block are used in finding motioninformation.

FIG. 9 is a schematic internal block diagram of an inter prediction unit700 having a spatial direction prediction mode applied thereto.

Referring to FIG. 9, an inter prediction unit 700 mainly includes adirect mode identifying unit 710, a spatial direct prediction performingunit 720, etc. And, the spatial direct prediction performing unit 720includes a first variable deriving unit 721, a second variable derivingunit 722 and a motion information predicting unit 723.

The direct mode identifying unit 710 identifies a prediction mode of acurrent slice. For instance, if a slice type of a current slice is Pslice or B slice, a direct mode is usable. In this case, it is able touse a direct mode flag indicating whether a temporal direct mode or aspatial direct mode in a direct mode will be used. The direct mode flagcan be obtained from a slice header. In case that the spatial directmode is applied according to the direct mode flag, it is able topreferentially obtain motion information of blocks neighbor to a currentblock. For instance, assuming that a block at a left side of a currentblock, a block at a top side and a block at a right top side are named aneighbor block A, a neighbor block B and a neighbor block C,respectively, it is able to obtain motion information of the neighborblocks A, B and C. The first variable deriving unit 721 is able toderive a reference picture index for List0 or List1 direction of thecurrent block using the motion information of the neighbor blocks. And,it is then able to derive a first variable based on the referencepicture index of the current block. In this case, the first variable canmean a variable (directZeroPredictionFlag) used in predicting a motionvector of the current block as a random value. For instance, a referencepicture index for the List0 or List1 direction of the current block canbe derived into a smallest value of reference picture indexes of theneighbor blocks. For this, the following formula (Formula 3) is usable.refIdxL0=MinPositive(refIdxL0A,MinPositive(refIdxL0B,refIdxL0C))refIdxL1=MinPositive(refIdxL1A,MinPositive(refIdxL1B,refIdxL1C))where, MinPositive(x,y)=Min(x,y)(x≥0 and y≥0)Max(x,y)(other cases)  Formula 3

For example, in detail, it becomes ‘MinPositive(0,1)=0’. In particular,in case that two valid indexes exist, it is able to obtain a smallervalue. Alternatively, it becomes ‘MinPositive(−1,0)=0’. Namely, in casethat one valid index exists, it is able to obtain a large value that isa valid index value. Alternatively, it becomes ‘MinPositive(−1,−1)=−1’.Namely, in case that two are not valid index at all, e.g., if bothneighbor blocks are blocks coded in an intra picture prediction mode ortwo neighbor blocks are not available, a large value ‘−1’ is obtained.Therefore, in order to obtain an invalid result value, at least onevalid value should not exist.

First of all, for an initial value of the first variable, it is able toset the first variable to 0. Moreover, in case that each referencepicture index for the derived List 0 and List1 directions is smallerthan 0, a reference picture index for the List0 or List1 direction ofthe current block can be set to 0. And, the first variable can be set toa value for indicating that a reference picture of the current blockdoes not exist. In this case, the case that each reference picture indexfor the derived List0 and List1 directions is smaller than 0 means acase that the neighbor block is a block coded in an intra pictureprediction mode or a case that the neighbor block is not available, forexample. In this case, by setting the first variable to 1, it is able toset a motion vector of the current block to 0.

Since three neighbor blocks are used for the present embodiment, in casethat all three neighbor blocks are coded in the intra picture predictionmode or not available, a reference picture index of the current blockmay have an invalid value of ‘−1’. Hence, if all reference pictureindexes of the current block are not available, the first variable canbe set to 1. In particular, if a reference picture to be used by acurrent block fails to exist, the first variable can be set to 1.

The second variable deriving unit 722 is able to derive a secondvariable using the motion information of the anchor block within theanchor picture. In this case, the second variable may mean a variablethat is used to predict a motion vector of a current block as a randomvalue. For instance, in case that the motion information of the anchorblock meets predetermined conditions, it is able to set the secondvariable to 1. If the second variable is set to 1, it is able to set amotion vector for the List0 or List1 direction of the current block to0. The predetermined conditions can include the following. First of all,a picture having a smallest reference picture index among referencepictures for the List1 direction should be a short-term referencepicture. Secondly, a reference index of a referred picture of the anchorblock should be set to 0. Thirdly, each of the horizontal and verticalcomponents of a motion vector of the anchor block should be equal to orsmaller than +1. Thus, if all the predetermined conditions are met, itis determined that it is close to a video having almost no motion. And,the motion vector of the current block is then set to 0.

The motion information predicting unit 723 is able to predict motioninformation of a current block based on the derived first and secondvariables. For instance, if the first variable is set to 1, it is ableto set the motion vector for the List0 or List1 of the current block to0. If the second variable is set to 1, it is able to set the motionvector for the List0 or List1 of the current block to 0. In this case,the setting to 0 or 1 is just exemplary. And, it is able to set thefirst or second variable to another predetermined value to use.

If the predetermined conditions are not met, it is able to derive motioninformation of a current block from motion information of neighborblocks within a current picture. For instance, in case of a motionvector, the motion vector deriving method of the skip macroblock isidentically applicable. A reference picture index of the current blockcan be found in a manner of calculating a minimum value among referencepicture indexes of the motion vectors located at left, top and right topsides and then setting the minimum value to the reference picture of thecurrent block.

A method of indicating whether a current macroblock is coded in a directmode is explained as follows. For this, it is understood that the samemethod is applicable to a sub-macroblock as well.

FIG. 10 is a block diagram of a process for decoding slice data usingskip or direct mode indication information.

Referring to FIG. 10, it is able to parse flag information indicatingwhether a current macroblock within a slice is a skip macroblock[S1000]. The flag information can be obtained from a slice layer. As aresult of parsing the flag information, if the current macroblock is theskip macroblock [‘yes 1’], it is able to perform decoding withoutparsing motion information and residual data [S1050]. Yet, if thecurrent macroblock is not the skip macroblock [‘no 1’], it is able toparse a block type of the current macroblock [S1010]. It is able toparse skip or direct mode indication information for each partition ofthe current macroblock according to the block type of the currentmacroblock [S1020]. In this case, the skip or direct mode indicationinformation may mean the information indicating whether the partition ofthe macroblock is coded in the skip mode or the direct mode. Thefollowing description is made on the assumption that a size of a currentmacroblock is 32×32. First of all, as a result of parsing currentmacroblock type information, if the current macroblock is coded in aninter picture prediction mode and a partition of the current macroblockis 16×32, 2 bits will be used as skip or direct mode indicationinformation. If a partition index 0 of a macroblock is coded in skip ordirect mode but a partition index 1 of the macroblock is not coded inthe skip or direct mode, it is able to obtain ‘10’ as skip or directmode indication information. After the skip or direct mode indicationinformation has been parsed, it is able to parse CBP coded blockpattern) information [S1030]. In this case, the CBP information can meanthe information indicating whether a current block includes residualdata. Therefore, by parsing the CBP information, it is able to knowwhether the partition of the current block is coded in the skip mode orthe direct mode. For instance, as a result of parsing the CBPinformation on the partition of the current macroblock, if ‘1’ isobtained, it is able to regard that the partition is coded in the directmode. Based on the skip or direct mode indication information, it isdetermined whether each partition of the current macroblock is coded inthe skip or direct mode. In case that the partition is not coded in theskip mode or the direct mode [‘no 2’], it is able to perform decoding byparsing motion information and residual data [S1040] [S1050]. Yet, incase of the partition coded in the skip mode or the direct mode [‘yes2’], whether the partition is coded in the skip mode or the direct modewill be determined based on the parsed CBP information [S1060]. Hence,in case of coding in the skip mode [‘yes 3’], it is able to performdecoding without parsing the motion information and the like [S1040]. Incase of coding in the direct mode [‘no 3’], after the residual data hasbeen parsed [S1070], it is able to perform decoding using the residualdata [S1050]. In case of coding in the direct mode, it is able to derivea motion vector in the same manner of the case of coding in the skipmode. It is able to use the direct mode if a slice type is a P slice aswell as a B slice.

If the slice type is the B slice, macroblock type information caninclude size information of a predicted block, prediction directioninformation and the like. Yet, if it is indicated that a partition of acurrent macroblock is coded in a skip or direct mode according to theskip or direct mode indication information, a motion vector of thepartition is derived. Hence, the prediction direction information of thepartition can be derived. In this case, it is able to regard that themacroblock type information includes unnecessary prediction directioninformation. Hence, by newly defining a macroblock type, it is intendedto efficiently perform decoding of the slice data using theabove-mentioned skip or direct mode indication information. Forinstance, it is able to set a macroblock type for a B slice to one ofB_direct_32×32, B_32×32, B_32×16, B_16×32 and B_16×16. Yet, in case thata macroblock type is reset, it is determined whether the partition ofthe current macroblock in FIG. 10 is coded in the skip mode or thedirect mode. If it is coded in the skip mode or the direct mode,decoding will be performed in the same process as explained in theforegoing description. If it is not coded in the skip mode or the directmode, information on a prediction direction of a macroblock will beparsed from a received bitstream as well as motion information andresidual data.

Accordingly, the present invention is applicable to video signalencoding/decoding.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A method of decoding a video signal bitstream bya decoding apparatus, the method comprising: constructing, by thedecoding apparatus, motion vector predictor candidates for a currentblock, the motion vector predictor candidates consisting of a motionvector of a top neighboring block and a motion vector of a leftneighboring block, the top neighboring block and the left neighboringblock being adjacent to the current block; obtaining, by the decodingapparatus, index information of the current block from the video signalbitstream, the index information specifying a motion vector predictorcandidate from among the motion vector predictor candidates; deriving,by the decoding apparatus, a motion vector predictor of the currentblock from the motion vector predictor candidates, the motion vectorpredictor of the current block being the motion vector predictorcandidate corresponding to the obtained index information; obtaining, bythe decoding apparatus, a motion vector difference of the current block;and decoding, by the decoding apparatus, the current block based on thederived motion vector predictor and the motion vector difference.
 2. Themethod of claim 1, wherein the left neighboring block is a block locatedat a left side of the current block and the top neighboring block is ablock located at an upper side of the current block.
 3. The method ofclaim 1, further comprising: obtaining, by the decoding apparatus,prediction mode information of the current block from the video signalbitstream; and wherein the prediction mode information indicates thatthe current block is coded in an inter mode.
 4. The method of claim 1,wherein decoding the current block includes: obtaining, by the decodingapparatus, residual data of the current block from the video signalbitstream, obtaining, by the decoding apparatus, predicted pixel valuesof the current block based on the motion vector predictor and the motionvector difference, and reconstructing, by the decoding apparatus, thecurrent block using the residual data and the predicted pixel values. 5.The method of claim 1, wherein decoding the current block includes:obtaining, by the decoding apparatus, a motion vector of the currentblock using on the motion vector predictor and the motion vectordifference of the current block, and performing, by the decodingapparatus, motion compensation for the current block using one or morereference pictures based on the obtained motion vector.
 6. The method ofclaim 1, further comprising: obtaining, by the decoding apparatus, skipmode indication information of the current block from the video signalbitstream; and wherein the skip mode indication information indicatesthat the current block is not coded in a skip mode.
 7. The method ofclaim 1, wherein a size of the current block is one of 16×16, 16×8,8×16, 8×8, 8×4, 4×8, or 4×4.